Morphological study of the gastrointestinal tract of the snow trout, Schizothorax esocinus (Actinopterygii: Cypriniformes)

ABSTRACT The present study aimed to investigate the macroscopic structure of the gastrointestinal tract (GIT) of Schizothorax esocinus Heckel, 1838. The surface architecture of the buccopharynx, oesophagus and the entire intestinal tract of S. esocinus has been examined under scanning electron microscope (SEM) after fixing in 2.5% glutaraldehyde buffered with 0.1 M sodium cacodylate at pH 7.3 for 18-48 hours and post-fixation for two hours at room temperature in 1% osmium tetra oxide buffered at pH 7.3 with 0.1 M cacodylate. The mucosal surface of buccopharynx, esophagus, intestinal bulb, and intestine reveal prominent longitudinal major or primary mucosal folds which are further subdivided into the series of irregular and well-circumscribed folds called minor or secondary folds. However, in the intestinal bulb and intestine, the longitudinal major or primary folds themselves form wavy or zigzagging patterns along the mucosal surface. The fine structure of the surface epithelium further shows that the apical surfaces of the epithelial cells are ped with finger-print like microridges, arranged in various patterns and regularly spaced. The rectal mucosa, on the other hand, displays a highly irregular type of major mucosal folds. The separation can’t be seen between major mucosal folds. A thin film of mucous spread over the mucosal folds and the numerous pores through which mucous cells release their content has also been noted along the rectal mucosa. This investigation suggests the possible role of different digestive organs in relation to feeding, digestion, storage, absorption, and various other physiological processes, thereby providing a knowledge necessary to the understanding of pathological or physiological alterations in both aquaculture and natural environment.

摘要
本研究旨在探究1838年Heckel命名的长丝裂腹鱼（Schizothorax esocinus Heckel, 1838）的胃肠道（gastrointestinal tract, GIT）大体结构。研究通过扫描电子显微镜（scanning electron microscope, SEM）对该鱼的口咽腔（buccopharynx）、食管（oesophagus）、肠球（intestinal bulb）及全肠道的表面结构进行观察：先以pH 7.3的0.1 mol/L二甲胂酸钠缓冲液配制的2.5%戊二醛固定样本18~48小时，随后于室温下采用pH 7.3的0.1 mol/L二甲胂酸钠缓冲液配制的1%四氧化锇进行后固定2小时。
口咽腔、食管、肠球及肠道的黏膜表面可见显著的纵向主（初级）黏膜褶皱，此类褶皱可进一步细分为一系列轮廓清晰的不规则次级（次要）黏膜褶皱。但在肠球与肠道中，纵向主（初级）黏膜褶皱自身会沿黏膜表面形成波浪状或锯齿状形态。表面上皮的超微结构进一步显示，上皮细胞的顶面覆盖有指纹状微脊，这些微脊以多种模式排列且间距规整。
而直肠黏膜的主（初级）黏膜褶皱则呈现高度不规则的形态，且褶皱之间无明显分界。此外，直肠黏膜表面还可见覆盖于黏膜褶皱上的薄层黏液，以及大量供黏液细胞释放内容物的孔隙。
本研究揭示了不同消化器官在摄食、消化、储存、吸收及其他多种生理过程中的潜在作用，可为理解水产养殖与自然环境中的病理及生理变化提供必要的理论支撑。